Chapter 48 - Guyton

Question 1

Explain the difference between fast and slow pain.

Answer 1

fast pain is felt within 0.1 sec and is sharp vs. slow pain which is felt after 1 sec and is throbbing, aching pain

Question 2

The pain receptors in the skin and other tissues are all ______ ______ _________.

Answer 2

free nerve endings

Question 3

Where are the free nerve ending pain receptors widespread?

Answer 3

superficial layers of the skin and in certain internal tissues, such as the periosteum, arterial walls, joint surfaces, and falx and tentorium in the cranial vault

Question 4

Which stimuli can elicit pain?

Answer 4

mechanical (fast/slow), thermal (fast/slow), chemical (slow)

Question 5

Chemicals that excite the chemical type of pain.

Answer 5

bradykinin, serotonin, histamine, potassium ions, acids, acetylcholine, and proteolytic enzymes

Question 6

Enhance the sensitivity of pain endings but do not directly excite them.

Answer 6

prostaglandins and substance P

Question 7

Do pain receptors adapt as other sensory receptors do?

Answer 7

no, in fact sometimes the sensitivity can actually increase as the pain progresses (hyperalgesia)

Question 8

T/F The tissue damage that has already occurred is the primary influencer of pain.

Answer 8

False. The rate of tissue damage is the most important determining factor of pain felt.

Question 9

This chemical causes the most pain and may be the single most responsible for causing the tissue damage type of pain.

Answer 9

bradykinin (also local increase in potassium ions and action of enzymes can contribute to pain)

Question 10

How can muscle spasm cause pain?

Answer 10

stimulates mechanosensitive pain receptors and also ischemia from restricting blood flow

Question 11

What is the fiber transmission for fast, sharp pain?

Answer 11

elicited by mechanical or thermal pain stimuli; transmitted in the peripheral nerves to the spinal cord by small type A-delta fibers at velocities between 6-30 m/sec

Question 12

What is the fiber transmission for slow, chronic type pain?

Answer 12

elicited mostly by chemical (can be mechanical or thermal stimuli); transmitted to the spinal cord by type C fibers at velocities between 0.5-2 m/sec

Question 13

What is the pathway for fast, sharp pain?

Answer 13

neospinothalmic tract (most fibers pass all the way to thalamus uninterrupted, glutamate is the neurotransmitter used)

Question 14

What is the pathway for slow, chronic pain?

Answer 14

paleospinothalmic tract (most fibers terminate in brain stem and then are relayed to brain, substance P is likely neurotransmitter)

Question 15

Neospinothalmic tract pathway.

Answer 15

on entering the cord, type A-delta fibers may travel up or down 1-3 segments and terminate on neurons in the dorsal horn; 2nd order neuron crosses to other side and passes to brain in anterolateral columns; some neurons terminate in reticular substance but most go to ventrobasal complex of thalamus; 3rd order neurons go to the cortex

Question 16

How can fast, sharp pain be localized?

Answer 16

in order to be highly localized free nerve endings need to be stimulated along with other tactile sensory receptors (dorsal column-medial lemniscal system)

Question 17

Paleospinothalmic tract pathway.

Answer 17

type C fibers terminate in lamina II and III of the spinal cord and make one or two local connections before giving rise to 2nd order neurons which cross immediately and pass to the brain in the anterolateral columns (only 10-25% of fibers terminate in thalamus); most fibers terminate diffusely in the reticular nuclei of the pons, medulla, and mesencephalon, tectal area of the mesencephalon, periaqueductal gray region, neurons project to intralaminar nuclei of the thalamus, hypothalamus and other basal brain regions

Question 18

Is slow pain localized?

Answer 18

poor localization, often only to the affected limb or part of the body

Question 19

Why is it nearly impossible to sleep when a person is in severe pain?

Answer 19

Electrical stimulation in the reticular areas of the brain stem and in the intralaminar nuclei of the thalamus, the areas where the slow-suffering type of pain terminates, has a strong arousal effect on nervous activity throughout the entire brain (brain’s principle arousal system).

Question 20

What is the significance of the cortex in the appreciation of pain?

Answer 20

removal of the somatic sensory areas of the cortex does not destroy the ability to perceive pain; cortex important for determining quality of pain

Question 21

Analgesia system in the brain and spinal cord.

Answer 21

brain can suppress pain fibers, periaqueductal gray area neurons send axons to the nucleus raphemagnus and the nucleus reticularis paragigantocellularis then to dorsal horns of the spinal cord, these neurons activate a pain inhibitory complex in the spinal cord

Question 22

At higher levels of the brain, which areas can be stimulated to suppress pain?

Answer 22

periventricular nuclei in the hypothalamus, lying
adjacent to the third ventricle, and, to a lesser
extent, the medial forebrain bundle, also in the hypothalamus

Question 23

__________ is believed to cause both presynaptic and postsynaptic inhibition of incoming type C and type A-delta pain fibers where they synapse in the dorsal horns.

Answer 23

Enkephalin

Question 24

About a dozen such opiate-like substances have now been found at different points of the nervous system; all are breakdown products of three large protein molecules:

Answer 24

proopiomelanocortin, proenkephalin, and prodynorphin

Question 25

Among the more important of these opiate-like substances are:

Answer 25

beta-endorphin (hypothalamus and pituitary); met-enkephalin, leuenkephalin, and dynorphin (brain stem and spinal cord)

Question 26

What is the “gate control hypothesis”?

Answer 26

stimulation of large type A-beta sensory fibers from peripheral tactile receptors can depress the transmission of pain signals (lateral inhibition of pain fiber by sensory fiber), this is why massage, liniments, and e-stem works

Question 27

What is referred pain?

Answer 27

pain from an internal organ that is perceived to originate from a distant area of skin, mechanism is intermingling of 2nd order neurons from the skin and viscera, viscera have few sensory fibers except for pain

Question 28

Common areas of referred and visceral pain.

Answer 28

localized to the dermatome of embryological origin; heart localized to the neck, shoulder, or arm; stomach localized to above the umbilicus; colon localized to below the umbilicus

Question 29

Essentially all visceral pain that originates in the thoracic and abdominal cavities is transmitted
through which type of fibers?

Answer 29

small type C pain fibers and, therefore, can transmit only the chronic-aching-suffering type of pain

Question 30

Causes of visceral pain.

Answer 30

ischemia, chemical irritation, spasm of a hollow viscus (cramps!), overdistension of a hollow viscus

Question 31

Almost any type of traumatizing, crushing, or stretching stimulus to the blood vessels of the ______ can cause headache.

Answer 31

meninges

Question 32

Pain sensitive areas of the brain:

Answer 32

dura, blood vessels of the dura, venous sinuses, middle meningeal artery

Question 33

Meningitis

Answer 33

inflammation of the meninges resulting in a severe headache

Question 34

Migraine

Answer 34

resulting from abnormal vascular phenomenon, vasospasm followed by prolonged vasodilation which causes stretchings of the coverings of the blood vessels

Question 35

Hangover

Answer 35

irritation of the meninges by alcohol breakdown products and additives

Question 36

Causes of extracranial headache (self-explanatory).

Answer 36

muscular spasm (tension headache), sinus headache, eye strain

Question 37

When do cold receptors respond?

Answer 37

from 7-44 degrees Celcius with the peak response at 25 degrees

Question 38

When do warm receptors respond?

Answer 38

from 30-49 degrees Celcius with the peak response at 44 degrees

Question 39

What is the mechanism of stimulation of thermal receptors?

Answer 39

changes the metabolic rate of the receptor, this changes the rate of intracellular reactions

Question 40

Do thermal receptors adapt?

Answer 40

yes, this explains the response to changes in temperature explains the extreme degree of heat one feels on first entering a tub of hot water and the extreme degree of cold felt on going from a heated room to the out-of-doors on a cold day

Question 41

Brown-Séquard syndrome

Answer 41

Characterized by loss of motor function (i.e. hemiparaplegia), loss of vibration sense and fine touch, loss of proprioception (position sense), loss of two-point discrimination, and signs of weakness on the ipsilateral (same side) of the spinal injury. This is a result of a lesion affecting the dorsal column-medial lemniscus tract, which carries fine (or light) touch fibers, conscious proprioception, vibration, pressure and 2-point discrimination, and the corticospinal tract, which carries motor fibers. On the contralateral (opposite side) of the lesion, there will be a loss of pain and temperature sensation and crude touch 1 or 2 segments below the level of the lesion.